Sustaining-rotor-equipped aircraft, including autorotatable rotor construction and the regulation of rotor blade pitch



May 27; 1947. J. DE LA clERvA 2,421,364

SUSTAINING-ROTOR-EQUPPED AIRCRAF T INCLUDING AUTOROTATABLE ROTOR CONSTRUCTION AND THE REGULATION OF ROTOR BLADE PTCH Filed Jan. l5, 1956 15 SheetS-Sheet l INVENTOR May 27. 1947. J. DE LA CIERVA 2,421.364 SUSTAINING-ROTOR-EQUIPPED AIRCRAFT INCLUDING AUTOROTATABLIE ROTOR CONSTRUCTION AND THE REGULATION OF ROTOR BLADE FITCH Filed Jan. 15, 1956 15 sheets-sheet 2 W Ma ATTORNEYJ May 27. 1947. J. DE LA cil-:RVA

SUSTAINI'NG-ROTOR-EQUIPPED AIRCRAFT INCLUDING yCONSTRUCTION AND THE REGULATION OF ROTOR BL Filed Jan. 15, 1956 C INVENTOR d. TTORNEYS May 27. 1947. 1 DE A (gn-RVA` 2,421,364

sUsTAINING-ROTOR-EOUIPPED AIRCRAFT INCLUDING AUTOROTATABLE ROTOR CONSTRUCTION AND THE REGULATION OF ROTOR BLADE FITCH Filed Jan. 15, 1956 15 Sheets-Sheet 4 /042 @D IQ) XNVENTOR WAM ATTQRNEYS May 27. 1947. J DE LA ClERvA 12,421,364

sUsTAINING-ROTOR-EQUIPPED AIRCRAFT INCLUDING AUTOEOTATADLE ROTOR CONSTRUCTION AND THE REGULATION OE ROTOR BLADE P ITCH Filed Jan. l5, 1956 15 sheeisqsheet 5 93 y 45 EL@ 99 445 J7 55 5.9 *J0 I Q E ff M 47 V 7 j mvENTo QZ/ww vf A ORNEY5 May 27- 1947- J. DE LA cil-:RVA 2,421,364

SUSTAINING-ROTOR-EQUIPPED AIRCRAFT NCLUDING' AUTOROTTABLE KOTOR CONSTRUCTION AND THE REGULATION OF ROTOR BLADE FITCH Filed Jan. l5, 1936 l5 Sheets-Sheet 6 l ya 4f y 57 55 39 jfl l .wb

y 5W I 1- INVENTOR .5f ATTORNE May 27. 1947. v J. DE A clERvA 2,421,364-

sUsTAINING-ROTOR-EOUIRPED AIRCRAFT INCLUDING AUTOROTATABLR ROTOR CONSTRUCTION AND TRE REGULATION OF ROTOR BLADE PITOH Filed Jan. 15, 1956 15 Sheets-Sheet 7 INVENTOR.

BY www ATTORNEYS May 27. 1947. J. DE LA cli-:RVA

CONSTRUCTION AND THE REGULATION OF RO Filed Jan. l5, 1956 SUSTAINING-ROTOR-EQUIPPED AIRCRAFT INCLUDING AUTOROTATABLE ROTOR TOR BLADE PITCH l5 Sheets-Sheet 8 wf/Mo? INVENTOR May 27. 1947. J. DE LA CIERVA 2,421,364 l SUSTAINIDIG-ROTOR-EQUIPPED AIRCRAFT INCLUDING AUTOROTATABLE ROTOR CONSTRUCTION AND THE REGULATION OF ROTOR BLADE PITCH FiledJan. 15, 1936 15 Sheets-Sheet 9 l j b OL/ ff L52 l L5,

INVVENTOR WWW ATTO R N EYS J. DE LA clERvA 2,421,364

UTOROTATABLE ROTOR May 27, 1947.

SUSTAINING-ROTOR-EQUIPPED AIRCRAFT INCLUDING A CONSTRUCTION AND THE REGULATION OF ROTOR BLADE FITCH Filed Jan. 15, 1956 l15 Sheets-Sheet l0 ahw t@ INVENTOR VMMM ATTORNEYJ May 27. 1947. J, DE LA cli-:RVA 2,421,364

SUSTAINING-ROTOR-EQUIPPED AIRCRAFT INCLUDING AUTOROTATABLE ROTOR CONSTRUCTION ND THE REGULATION OF ROTOR BLADE PITCH Filed Jan. 15`, 1956 15 Sheets-Sheet ll (7g2/ Y] Ja 0 y of@ 5 d f jig,

mld.' v f I Z cfa cf Zin/a 064 l' J 10C! nl t I INVENTOR X" @A fm f1/Mm /77 ATTORNEY5 4 May 27 1947- J. DE LA cil-:RVA 2,421,364

SUSTAINING-ROTOR-EQUIPPED AIRCRAFT :INCLUDING AUTOROTATABLE ROTOR CONSTRUCTION AND THE REGULATION OF KOTOR BLADE FITCH Filed Jan. 15, 1936 15 Sheets-Sheet l2 A Wg INVENTOR BY ab f/ @wad @bf- MM ATTORNEY May 27. 1947. 1 DE A CXERVA 2,421,364

SUSTAINING-ROTOR-EQUIPPED AIRCRAFT INCLUDING AUTOROTATABLE ROTOR CONSTRUCTION AND THE REGULATION OF ROTOR BLADE PITCH Filed Jan. 15, 1936 15 Sheets-Sheet 15 INVENTOR :4 Ik) ATTORNEY1 'May 27. 1947. J DE LA CIERVA 2,421,364

SUSTAINING-ROTOREQUIPPED AIRCRAFT INCLUDING UTOROTATABLE ROTOR CONSTRUCTION AND THE REGULATION OF ROTOR BLADE FITCH Filed Jan. l5, 1936 l5 Sheets-Sheet 14 lNvENToR- I Lam BY? wk www ATTORNEYS May 27. 1947. J. DE LA clERvA 2,421,364

SUSTAINING-ROTOR-EQUIPPED AIRCRAFT INCLUDING AUTOROTATABLE ROTOR CONSTRUCTION AND THE REGULATION OF ROTOR BLADE PITCH med Jan. 15, 193e 15 sheets-sheet 15 INVENTOR TTORNEY Patented May'27, 1947 SUSTAINING-ROTOR-EQUIPPED AIRCRAFT, INCLUDING AUTOROTATABLE ROT-OR; CONSTRUCTION AND THE REGULTJION OF ROTOR BLADE PITCH Juan de la Cierva, Madrid, Spain, .assignon by mesne assignments, to Autogiro Company of America, a corporation of 'Delaware Application. January `15, 1935, Serial No. .5S-,292. In Great Britain January 16, 1936 60. Claims. .1

The present invention relates to sustainingrotor-equipped aircraft, including autorotatable rotor construction and the. regulation of rotor blade pitch, and is. particularly useful in .that type of craft. wherein the, principalmeans of sup.- DeOrt in flight .consists of a system of rotative wngsor blades, hereinafter referred to as arotor, mounted for free rotation about, a. substantially vertical axis and adapted for autorotation in flight under the influence, ofthe night, wind; `and in `meansof forward. propulsion are provided comprising. one or more engines .driving an airscrew or airscrews, or the like. propulsive devices, together With means `for imparting an initial rotation tothe rotor, usually referred to asarotor starter, which may comprise a disconnectibledrivingconnection between the said ,ene gine and the rotor adapted to apply a. torque t saidrotor (asin Pecker U. `S..1?atent 1,999,636).

More particularly, the invention is .especially adapted toairCrait having `sustaining rotors of the kind referred to, in which the individual bladesare, attachedto the. hub or centralmember of the rotor by vilexible .or .articular connections whichy permiteachblade to swing. up and down substantially in a place. containing. therotor axis. The purposes and advantages oi the invention will be. best. understood after some consideration of the general state of this art.

In .aircraft of the kind above described, the blades are generally attached to the hub each by atV least .two independent articulations allowing free, or damped motion. of4 the blades .both in a plane approximately containing the axis of rotation of. .the rotor and. in a plane approximately perpendicular to the rotor axis. These articulations :may Vbe referred to, respectively, as flapping hinges and drag hinges, the rst being thosearonndV which allor the greater part. of the blade oscillation takes place when. the blade swings in a. plane. containing or parallel .to the axis, of rotation, and the second those around which .all or. mQSt of the oscillation takes place when the blade swings in a plane perpendicular to theV axis of rotation of. the rotor or approximately fore-andeaft in thegeneral path of rotation.. Howeven, there are. alternative Ways of adapting the rotor to accommodate or compensate for .'difierential. flight forces. For example, the yieldability ofthe rotor in the napping sense, sufcierit to accommodate differential lift effects (such ijor' instance as are `due to translational night) may be secured by llexible constructionor by articular joints, as4 hereinabove. mentioned, or by a combination .o both, ashereinaiter described with, refenence to. .the drawings..

A fnrther deyelopment of this type A.of craft, havingan important. relationship to the present invention,l isdisclosed ,in my prior British Patent speci'cationNo., `420,322, vand Ain the corresponding. United States. application, `Serial' No. 738;349, filed' August, 193.4, which` issued' July 3l, 1945, as Alfaterlt. 2,380,583, wherein there is described mechanism` to enable. airciaitof this'kindto takeoff! withoutany run. on the ground, the .operation of. which essentially consists in diminishing the pitch angle of the .blades during the .application of the. Starting torque Aby means. of the .motor starter, to an angle corresponding substantially to the minimum aerodynamical (rotational) drag, and thereafter increasing the pitch angle,

simultaneously with the declutching ofthe rotor starter transmission, to substantially the normal antorotational' value suitable for forward flight; A take-oilY accomplished in` this way, with little orno runmay be conveniently referred to as a direct take-off.

Such. aircraft'may employV various expediente for controlling. Aand regulating the rotor Ablade pitch angle,r and the devices for this purpose fall naturally into. two groups. In the. first group, the pitch angle is positively regulated by mechanism controlled more or less independently of the forces acting on the'rotor blades'themselves either manually .bythe pilot (in which case the control' may be rendered atleast semi-automatic bythe interposition of regulating devices, orelse by means interconnected' with other aircraft controls, e.. g4., the starterV clutch, rotor brake and/or wheel :brake controls, or with the undercarriage (the control being ,atI least semi-automatic this case also) examples of such semi-automatic regulators', interconnectiorrs,` etc., being disclosed hereinafter and also in myA copending application SerialNo. 59,293--led January 15, 1936, which issued as `Patent No. 2,155,409 on Apri-125, 1939?.

Pitch controlling andregulatingdevices falling in this 4first group Vmight -bereferred `to as mechan'ical.7 y

The secondgroup voli pitchcontrolling and `reg-- ulating devices comprise those Iinvvliielr tlf1-e-=pitch-V angle is controlled in a -fullyautomatic `manner in accordance with -tlie-balance of forces experi encedgbyflthegrotorblades themselves, i. e., the applied torque, `centrifugal force, aerodynamic lift,drag andpitching moment and' inertia forces and `bythe elastic cha-racteristicsv of the rotor blades. Devices falling in thiscategory may-be referred' to as automatici An `object of.' this'invention provide an ilmproved and more; efllcient rotor partici-ilarly adapted for obtaining the. most renicient direct take-off possible, and the invention will be hereinafter described with special reference to its peculiarly advantageous co-operation with the direct take-off type of machine, although a full disclosure of such machine is not included herein as it will be found in the said Patent No. 2,380,583'.

In the process of accomplishing a direct takeoif, from the instant at which the pitch increase begins until autorotation is established, the rotor operates under a continuously changing regime, characterised by varying inflow, which, starting at zero, has at first a rapidly increasing positive (downward) value, reaching a peak and thereafter declining more slowly to Zero again and nally reversing its sign as autorotaton establishes itself.

If, for take-od, the blade pitch angle is increased almost instantaneously from about Zero to an autorotative value of say or 6 degrees, the thrust of the rotor immediately jumps from nothing to a large (peak) value much exceeding the Weight of the aircraft, on account of the initial absence of iniiow, and as the (downward) inflow builds up the thrust falls sharply and continues to fall as the rotational speed falls. Thus at the beginning of the take-off there is a violent upward acceleration which is followed. by a relatively rapid falling off of lifting effort, which may give rise to a loss of height from the maximum attained, before autorotative night is established.

An object of the present invenion is to obviate the above-mentioned disadvantages.

According to this invention, in an aircraft of the kind referred to, I may provide means operating independently of the pilots volition for regulating the rate of change of blade pitch angle during the period of changing regime of airflow from the instant of initiating disengagement of the starter clutch until autorotation is established and for limiting the maximum pitch angle attained, in such a way as to minimise fluctuations of the thrust delivered by the rotor and to set maximum limits on the Vthrust and drag torque of the rotor during the said period of changing regime.

In a preferred method of operation the pitch angle is so regulated that the pitch angle during the initial regime of accelerated (downward) airflow is such as to set a limit on the peak thrust delivered which limit is low enough substantially to eliminate all shock eiect.

Preferably also, the pitch angle is regulated according to such a method that an upper limit is set on the mean drag torque of the rotor, during the whole period of changing regime, said limit being low enough to ensure that the rotational speed exceeds the minimum requisite for autorotation at all times within the said period of changing regime.

With rotors of the -characteristics hitherto usual, the mean blade pitch angle, averaged over the whole period of changing regime, should not exceed 8 measured from no lift.

Means are preferably provided, which are brought into action on the initiation of withdrawal of the starter clutch and thereupon control and regulate the rotor blade pitch angle independently of the volition of the pilot in such a way that the pitch angle is increased from about zero to a certain maximum value and eventually to a desired value within the autorotative range of pitch angle (which value may be less than said maximum value, said means utilising either a timing device operative to impose a predetermined rate of change on variation of pitch angle or an automatic pitch changing device or a type, the pitch changing mechanism may include a timing device, e. g., a damped spring, operative to eifect an increase of blade pitch angle in a predetermined manner independently of the pilots volition on disengagement of the starter clutch.

Where, however, the pitch is controlled by automatic means, operative to increase the pitch angle on the disengagement of the starter clutch, which clutch is normally biased to disengaged position, the disengagement of the clutch may be regulated by a timing device, e. g., a damped spring acting independently of the pilots volition.

Alternatively, the action of the automatic pitch changing means itself may be regulated by a timing device, at least as long as the pitch angle is less than in normal autorotation.

I have found that the optimum delay in the initial increase of pitch angle is such that a value at least great enough for normal autorotation is attained in about 0.3 second.

According t0 a feature of the invention, the rotor may have automatic" pitch changing means so operative that a decrease of pitch angle is associated with an increase of the ratio thrust/centrifugal force and vice versa.

The effect of this is to prolong the direct lift effect by slowing down the rate of decrease of thrust after the peak value has been passed as hereinafter more fully explained.

How the foregoing, together with such other objects and advantages as are incidentl to the invention, are obtained will be further evident after perusal of the following description of the structural embodiments of the invenion illustrated in the accompanying drawings, wherein:

Fig. 1 is a general view in side elevation of an aircraft incorporating one embodiment of the present invention.

Fig. 2 is another general view of the same in plan.

Fig. 3 is a further general View of the same in front elevation.

Fig. 4 is a diagrammatic representation in side elevation of the Starter clutch elements of the aircraft.

Fig. 5 is a view to an enlarged scale in central longitudinal vertical section of the rotor head and blade root articulation of the aircraft of Figs. 1 to 3.

Fig. 6 is a detail view in section taken along the line 6 6 of Fig. 5.

Fig. 7 is a diagrammatic detailed view to an enlarged scale generally in side elevation of the control mechanism of the starter clutch and rotor blade pitch changing gear.

Fig. 8 is a detail view of a modication corresponding to a part of Fig. 7.

Fig. 9 is a view similar to Fig. '7 illustrating a modication.

Fig 1G shows a detail View of Fig. 9 in section taken along the line iii-iii of Fig. 9.

Fig. 11 is a detail view in side elevation illustrating a further modication of the mechanism of Figs. 7 or 9.

Fig. 12 is a view similar to Fig. 11 illustrating a modification of the mechanism of Fig. 11.

Fig. 13 is a view in side elevation, partly in section, of the top of the rotor hub and the vblade root articulation according to a second embodiment of said featuresof the invention.

Fig. 14 is a sectional view taken along the lline Hl-M of Fig, 13,

Fig. 15 is a somewhat diagrammatic representation in isometric projection of a` rotor hub and blade of the kind shown in Figs. 13 and 14, illus.- trative of the operation thereof.

Fig. 16 is asomewhat diagrammatic view-in side elevation, similar to Fig. 13, of the top ofa'rotor hub and blade root articulation according to another embodiment of said features of the invention. v

Fig. 15a, is a diagrammatic skeleton View in isometric projection, generallysimilar to Fig. 15, showing the position of the axes of the various parts of the rotor hub and blade articulation of the structure shown in Fig. 16, illustrative ofthe operation thereof.

Fig. 17 is a somewhat diagrammatic View in plan of a rotor hub and blade root articulation according to a modification of the showing of Figs. 13 to 15.

Fig. 18 is a view of the same in side elevation.

Fig. 19 is a view. in section taken along the line iS-l of Figs. 17 and 18.

Figs. 20, 21 and 22 are views similar to Figs. 17, 18 and 19 respectively showing amodied disu position of the blade articulation axes; Fig. 20 being in plan; Fig. 21 in side elevation; and Fig. 22 in section taken along the line 2.2--22 of Figs. 20, 21.

Fig.. 23 `is a somewhat diagrammatic view in isometric projection representing a rotor blade and a flapping pivot of arotor blade assembly of the kind shown in Figs. 1.7 to 22 to illustrate the effect of exibility of the `rotor blade in the radial-.axial plane.

Fig. 24 is a somewhat diagrammatic view in side elevation, similar to Fig. 13, of the top of a rotor hub and blade root articulation according to another embodiment of said .features of the invention.

Fig. 24a is a diagrammatic skeleton View `in isometric projection, generally similar to Fig. .15 or Fig. 16a, showing the .position ofthe axes of the various parts of the rotor hub and blade articulation ofthe structure shown in Fig. 24., being illustrative of the operation thereof.

Figs. 25 to 28 are further diagrammatic views of the embodiment of Fig, 24, ,these views being in plan; Figs. 25, 2.6 and v27 krespectively illustrating different modes of bladedisplacement; and

Fig. 28 illustrating the same mode of blade displacement as Fig. 26 inthe assumed case in which the flapping pivots intersect the rotational axis instead of being offset therefrom.

Figs. 29 to 31 are general views of an aircraft incorporating the second general embodiment of the invention according to any of Figs. .13 to 28, Fig. 29 being in side elevation, Fig. 30 in plan and Fig. 31 in front elevation.

Fig. 32 shows diagrammatically in side eleva.-

tion an .aircraft according to the .present invenn aircraft is supported on main wheels 61 and a tail wheel 08, the former beingmounted on theV usual undercarriage structure consisting of tele scopic struts 83 and radius rods 8.4, y85. Therotor, consisting of three elongated -blades 'i0 and a rotor head assembly described below with ref,- erence to Fig. 5, is carried on a rotor supporting pylon structureconsisting of struts G9, G9a. Various typical aeroformproles for the blades, capable of autorotation, are shown in Figures 6, 1,5, 16a, 19, and 22.

For imparting initial rotation to the rotor before flight there is provided a `transmission from the engine to the rotor comprising a horizontal shaft .85 coupled to the engine and an upright shaft 38 connected through gearing to the rotor hub, the rearward and lower ends .respectively of shafts 8B, 3B being received within a housing- 'l, where they are coupled .through a clutch and gearing, the elements of which are diagrammatioally shown in Fig. 4. The starter clutch is controlled by a lever 95 keyed on a shaft 95 and `biased t0 clutch disengaging position by a spring 9'! and a lever 95 is connected by a rod 98 through the mechanism shown in Fig. 7 to a tension transe mitting element 33 enclosed within a sheathtd and connected to a hand lever 35.

Control of the aircraft in flight is by means cf a universally rockable control column .19 which is connected to the rotor head by means of rods I9, |23, longitudinal control being effected by an endwise movement of the rod |20, which is con-A nected to the column 'l0 by means of a bellcrank |32 and link |33 and the lateral control being effected by an endwise movement of the rod i9, which is connected to the column 19 by means of a crank |3ii (see Fig. 3) mounted on a longitudinal rocking shaft |3| on which the column i9 is pivoted for longitudinal movements and which is rotated by lateral movements of the control column.

Referring now to Fig. 4; a shaft 85 drives the shaft through a clutch 80, and a bevel gear pair 9|, S2. The clutch member Sil is fast on the shaft of the bevel gear 9| and the clutch member 89 is slidable on the shaft 86, `the end of which is spigotted into the shaft of the gear 3| and is movable by means of a striking lever Sil engaging in the groove of a thrust collar 93 secured to the member 85. The external lever S6 already described is secured on the shaft 95 of the lever 94.

Referring to Figs. 5 and 6; the rotor head assembly comprises an apex member |0| which is secured to the pylori struts 53, Eea. The member |0| terminates upwardly in a tubular axle member |02 on which is rotatable by means of bearings |04 a rotor hub |03. The latter member comprises lateral pivot lugs |05 supporting the flapping pivot pins |05 on which are rotatably mounted drag links |01 supporting drag pivot pins |58. On the latter are rotatably mounted forked blade root'members les supporting the roots v| l0 of the blades 10.

To the lower end of the hub member |53 is secured a gear ring |25 meshing with a pinion |26 enclosed within a housing |21. Pinion S25 is mounted on a short shaft |28 journaled within the housing |21 and connected at its lower end by means of a joint |29 with the upright shaft 03 of the star-ter drive transmission.

In `order to enable the pitch angles of the rotor blades to be varied the blade root element is rotatable on the `root member |09 and vcarries Valever `the disposition of which is shown more clearly in Fig. 6, in which the direction of rotation of the rotor is indicated by an arrow, and this lever is universally articulated at I2 to a rod H3, the raising or lowering of which alters the pitch angles of the rotor blade. In order that the apping of the blade about the pivot |03 shall not introduce appreciable variations of pitch angle the articulation pivot ||2 is situated on the axis of the pivot pin |06 when the blade is set at its normal flying pitch angle.

Movement of the rods H3 to control the blade pitch angle is eifected by pivoting their lower ends to lugs ||4 mounted on a ring ||5 which rotates with the rotor, being supported by means of bearings llt on a non-rotative collar ||1 carried by a sleeve i8 which is slidable but nonrotatable on the axle member |32.

Variation of the pitch angles of all the blades together is effected by raising and lowering the sleeve H3, which is connected for this purpose to a rod 45, the lower end of which is actuated by the mechanism shown in Fig. 7. The lever is placed forwardly of the blade axis with respect to the direction of rotation (see Fig. 6) so that an increase of blade pitch angle is produced by raising the rod 45 and the elements ||3 to ||B and vice versa.

Longitudinal and lateral control of the aircraft in flight is obtained by diiferential variation of the blade pitch angles and this is effected by tilting the collar l1 laterally and longitudinally, for which purpose it is universally rockably mounted on the sleeve ||8 by means of a spherical joint and its tilt is controlled by means of the rods H9, |23 operating through linkages |2|, |22 and |23, |24 respectively. As the mechanism for obtaining longitudinal and lateral ying control by differential pitch variation is not per se part of the present invention it will not be further described. This mechanism is fully described in my copending application for patent, Serial No. 698,372, led November 16, 1933, corresponding to British Patent No. 410,532, which copending application issued on July 31, 1945, as Patent 2,380,582.

Referring to Fig. '1: the lower end of the pitch controlling rod 45 is guided in a support 4E, andv terminates in a stud 44 engaging a curved slot 43 formed in a cam plate 3| pivoted on a fixed point at 32 and including a projection 3.6 engageable by a catch 31. The latter is biased to a position of engagement with projection 36 by a spring 33 acting on an abutment 39 in which the catch 31 is slidable and the said catch is withdrawable from the engaging .position by means of a tension element 4i! enclosed in a flexible sheath 4| and connected to a hand lever 42. Cam plate 3| is also connected by means or a tension element 33 enclosed within a flexible sheath 34 to the hand lever 35.

The cam plate is further connected by means oi a rod |03 pivoted to the cam plate at 3!! and a bell crank 93 with the starter clutch actuating rod 98 (see Fig. l). Cam plate 3| is also connected to a spring loaded dashpot device comprising an oil-filled cylinder 43 anchored at a xed point 43a, within which is a slidable piston 48 provided with oil throttling orifices 5| and biased by a spring 53, the piston being connected with the cam plate 3| by means of a rod 41 slidably guided in the end of cylinder 49 and pivoted to the cam plate 3| at 30.

vThe cam slot 43 is so shaped that when the cam plate 3| is rocked in a Conner-clockwise direction from the position shown in Fig. 7 the pitch controlling rod 45 is raised, thereby increasing the blade pitch angle.

The operation of this mechanism is as follows:

To engage the clutch the lever 35 is rocked in. a clockwise direction. The motion of lever 35 is communicated by the tension connection 33 to the: cam plate 3|, which is thereby rocked in a clock--v wise direction. The connection 41 raises the piston 48 and puts the spring 5|) under compression' and the connection 99, |00 moves the rod 98 to the left and rocks the clutch operating lever 96 in the direction for engaging the clutch (Fig. 4). At the same time the stud 44 is brought to the left-hand end of the cam slot 43, thus lowering the rod 45 and decreasing the rotor blade pitch angle to its minimum limit, which should be substantially zero. The clockwise movement of the cam plate 3| causes the projection 36 thereof to spring over the catch 31 and engage therewith, so that the cam plate and with it the pitch varying and clutch controlling mechanisms are locked in the position shown in Fig. '1 with the pitch angle at minimum value and the clutch engaged.

On depressing the release lever 42 the catch 31 is withdrawn from the projection 36, whereupon the cam plate 3| is rotated in a counterclockwise direction by the action of the spring 50 assisted by the clutch lever return spring 91 (see Fig. 4), thus disengaging the clutch and increasing the pitch angle from its minimum to its maximum value as the stud 44 travels along the slot 43. The rate at which this takes place is independent of the volition of the pilot and is determined solely by the characteristics of the dashpot 4'8 to 52, which introduces a certain delay in the disengagement of the clutch and the increase of pitch angle. The damping action of the dashpot ensures that the counter-clockwise rotation of the cam plate 3| takes place at a substantially constant speed and further the rate of change of blade pitch angle is regulated at every instant of this process by the slope of the cam slot 43 from point to point of its length.

It will be seen that the cam slot of Fig. '1 is designed to produce a somewhat more rapid increase of pitch at the beginning of the process than towards the end as it is desirable to have a fairly rapid increase of pitch angle at rst in order to generate an adequate upward thrust on the rotor for lifting the machine from the ground before the rotational speed has sensibly decreased and thereafter to increase the pitch angle somewhat more slowly in order to maintain the thrust as the rotational speed of the rotor decreases and the downward iniiow through the rotor disc accelerates. At the same time the initial rate of -pitch increase must not be so great that an excessive peak thrust is developed by reason of the absence of inflow through the disc at the beginning of the process.

In order however to obtain the maximum benet of the temporary direct lift effect, it is desirable to increase the pitch angle towards the end of the process to a value somewhat greater than that required for normal autorotative flight, so as to maintain the thrust as the rotational speed of the rotor falls and for this purpose a modified cam slot of the kind shown in Fig- 8 may be used. In this case the cam slot 43 has a distinct hump at 43aI and when the stud 44 passes over the hump 43a the blade pitch angle attains its maximum value, being thereafter decreased to its normal autorotative flying value when the 9,. stud t reaches the right-hand end of the, slot cl3.

In the foregoing construction the delaying action of the dashpot device is appliedto the disengagement of the clutch as well as to the increasing of the blade pitch angle. This feature is on the whole desirable but is not universalh7 necessary and in certain aircraft it may be advisable for the disengagement to be undamped, in which case the modified construction shown in Figs. 9 and 10 may be adopted. This diners from that shown inv Fig. '7 in that the clutch op-' erating mechanism 98, Hill is not connected direct to the cam plate 3i but toan auxiliary lever :'iizr mounted on the same pivot 52 as the cam plate 3i In this case also the tension element t3 of the clutch engaging lever 35 is attachedto the lever 54m and the projection 35 engaged bythe catch 3l is formed on the lever 31x.

In order that the clockwiseV movement of the vhand lever to engage the clutchshall also set the blade pitch angle to a minimum, the lever Six engages a projection 3io formed on the cam plate di, whereby clockwise rotation of the lever 3fm is communicated to the cam plate 3l. When the catch tl is released disengagement of the clutch under the action of the return spring 9i of Fig. 4 takes place without damping restraint and the release of the projection tia allo-ws the dashpot device 4l to 52 to rotate the cam plate 3l in the counter-clockwise direction to increase the pitch at a predetermined rate independent of the pilots volition, as already described in connection with Fig. '7. Thus, the effect is equivalent to a sequential operation, in that the clutch is fully released before completion ofthe pitch-increasing action of the cam plate.

Figs. 11 and 12 illustrate a modification in which the release device 3l to lil is interconnected with the pilots control column 19 in such a way that a backward movement of the control column from the fully forward position (in which the angle of incidence of the rotor as a whole is a minimum) automatically releases the catch 3l to allow the clutch to disengage and the pitch angle to increase, or alternatively in such. a way `that Ythe control column is locked in the fully forward position until the hand release lever d?.

is pressed down to release the catch 3l.

` In Fig. 11 the tension element 49 connected to the catch 91 is connected at its other end to a hook l-i engageable by a catch 11 pivoted on the control column 'i9 and biased to engaging position by a spring i8. When the control column is moved into most forward position the catch 'il springs over the hook 'i9 and engages therewith, so that on moving the control column back from this position the tension element lil is pulled to release the catch 3l. v

On the other hand in Fig. 12 the tension element 4S is connected as before to the hand release lever i2 on which is formed a hook 'l2 engaging a catch 13 connected by means of a flexibly sheathed tension element l5 with the control column i3 and biased to engaging position by means of a spring "ill, In this arrangement on the movement of the control column into the fully forward position the catch "i3 springs over and engages with the hook l2, thus locking the'controlcolumn in the forward position until the hook 12' is released from catch 'i3 by depressing the knob of the release lever 92.

A second general embodiment ofthe invention is illustrated in Figs. 13 to 31. The aircraft, of which general views fromthree aspectsare shown 10 in Figs. 29 to 31, is in most respects similar to the aircraft in Figs. 1 to 3, the chief difference in the aircraft considered as a whole being in the arrangement of the rotor head and controls. In this instance, control in flight is effected by inclining the rotor bodily as a whole. The rotor mounting pylon 69, 69a terminates man apex member I 39 to which is universally pivoted an axis.r member 31 on which is rotatably supported theihub member 53. The universal pivots connectingy the axis member ISI and the apex member E35 may be, enclosed within the former of these members, or may be located therebelow as shown in dotted lines in Fig. 29 of the drawings. The bearings on which the hub 53 is freely rotatably mounted are enclosed within the hub and do not appear on the drawings. MechanismY of this kind is fully described in my co-pending application for patent, Serial No. 645,985, filed December 6, 1932, corresponding to British Patent No. 39.3,-

976, which c-opending application issued on July 31, 1945, as Patent 2,380,580. The axis member itl is connected for control purposes to a hanging pilots control lever |32 and as the means for controlling the aircraft in flight are not per se part of the present invention they are not further illustrated or described herein but a description of the mounting of the control lever will be lfound in my copending application, Serial No. 59,293, led January 15, 1936, which copending application issued` on April 25, 1939, as Patent 2,155,409. As in the previous instance, the rotor hub has xed to its lower extremity a ring gear IE5 meshed with a pinion |23 contained within a housing |21, the latter being supported on the axis member i3! and as before the pinion |26 is connected tc the upper extremity of the upright shaft of the rotor starting transmission.

The connections of the rotor blades 1l] to the rotor hub are shown more'clearly in Figs. 13, 14. The rotor hub 53 terminates upwardly in lugs 53a: in which are mounted flapping pivot pins .54. On these are articulated drag links 55 each terminating in a drag pivot pin or trunnion on which is rotatably mounted by means of bearings (not shown) a drag pivot housing 5'6 terminating in a ,flange for attachment to the hanged inner end of blade root tting 5l to which is secured a rotor blade lil, the latter being omitted from Fig. 13 but shown in Figs. 29 to 31. The axis of the drag pivot pin (termed alpha axis) is shown in Fig. 13 at aand it Will be seen that this axis is inclined upwardly and outwardly at an acute angle to the longitudinal blade axis b-b.

The result of this arrangement is that movement of the blade on the drag pivot is associated with a change in blade pitch angle such that when the blade lags behind its normal mean radial position, the pitch angle is decreased and vice versa. By this means an automatic control of pitch angle during the starting of thefrotor and the take-off is obtained, the effect of the application of the starting torquetothe rotor causing the blade to lag and therefore decrease its pitch angle,

whereas when the starting torque vanishes on the disengagement of the starter clutch, the blade swings about its drag pivot approximately into its normal mean radial position with a consequent drag pivot housing 56 and the drag link 55. This 

